The present invention generally relates to a size detecting arrangement and more particularly, to an arrangement for optically detecting sizes of original documents, for example, in a copying apparatus and the like.
Recently, in the field of copying apparatuses, rapid progress has been made for the an automatic detection of original document sizes, with various systems being proposed therefor described below,
(i) A light emitting device and a light receiving device are respectively provided at the sides of an original document cover and a copying apparatus main body under an original document platform or vice versa so as to confront each other, and the sizes of the original documents are detected based upon the magnitude information of the output obtained at the light receiving device.
(ii) Sizes of original documents are detected based on the state of conduction between an electrically conductive rubber material provided on the original document cover and a transparent electrode provided at the main body of the copying apparatus.
(iii) A light emitting device for projecting light from the main body of the copying apparatus towards an original document on an original document platform and a light receiving device for receiving light reflected from the original document are provided for the detection of the original document sizes based upon the magnitude information of the output of the light receiving device.
(iv) A light emitting device for projecting light from the copying apparatus main body towards the original document cover in response to a function for turning the original document cover to a closed position, and a light receiving device for receiving light returning from a light returning reflecting member disposed on the original document cover, are provided for detecting the original document sizes based on the magnitude information of the output of the light receiving device.
In the system of the above item (i), there are disadvantages in problems arise due to invluence from the turning of the original document cover towards the open or closed position, since either one of the light emitting device or the light receiving device is provided at the side of the original document cover and the light receiving element which directly receives light from an exposure lamp for illuminating the original document is liable to be deteriorated.
The system in the above item (ii) is also inconvenient in that the detection of the size of the original document can not be effected with respect to an original document of a book-type, through which an electrical conduction can not be established.
In the system of item (iii), it becomes difficult to detect sizes with respect to original documents that have poor reflecting efficiency.
Meanwhile, in the system of item (iv), since the light emitting device and the light receiving device are disposed at generally the same position, with the reflected light being received by returning via an optical path through which the emitted light has passed, there is a possibility that the output of the light receiving device gives information different from the actual document size due to the irregular reflecting reflection of light from the original document, thus resulting in malfunctions of the size detecting arrangement.